1. Field of the Invention
The present invention relates to an organic electroluminescent display device which forms an organic light emitting layer between a pair of electrodes and emits light by applying an electric field to the organic light emitting layer by the pair of electrodes, and more particularly to an organic electroluminescent display device which can repair a black-dot defective pixel or a bright-failure defective pixel formed in the inside of a display region to form an light emitting pixel and a method for repairing such a defective pixel.
2. Description of Related Art
Recently, as a flat panel type display device, a liquid crystal display device (LCD), a plasma display device (PDP), a field emission type display device (FED), an organic electroluminescent display device (OLED) or the like has been commercialized and has been studied for commercialization. Among these display devices, the organic electroluminescent display device is an extremely prospective display device as a display device for future generation as a typical example of a thin and light-weighted emissive display device. The organic electroluminescent display device is classified into a so-called bottom-emission-type display device and a top-emission-type display device.
The bottom-emission-type organic electroluminescent display device constitutes an organic light emitting element by a light emitting mechanism which is constructed by sequentially stacking a transparent conductive thin film made of ITO (In—Ti—O) or IZO (In—Zn—O) which constitutes a first electrode or one electrode, an organic multi-layered film which emits light when an electric field is applied thereto (also referred to as organic light emitting layer), and a reflective metal electrode which constitutes a second electrode or another electrode on an insulating substrate which is preferably formed of a glass substrate. A large number of these organic light emitting elements are arranged in a matrix array, another substrate which is also referred to as a sealing can is provided in a state that another substrate covers the stacked structure, and the above-mentioned light emitting structure is insulated from an external atmosphere.
Further, by applying an electric field between both electrodes in a state that the transparent electrode is used as an anode and the metal electrode is used as a cathode, for example, careers (electrons and holes) are injected into the organic multi-layered film and this organic multi-layered film emits light. The emitted light is radiated to the outside from a glass substrate side.
On the other hand, in the top emission-type organic electroluminescent display device, in a state that the above-mentioned one electrode is formed of a metal electrode having the reflectance and another electrode is formed of a transparent electrode such as an ITO film, by applying an electric field between both electrodes, the organic multi-layered film emits light and the emitted light is radiated from the above-mentioned another electrode side. In the top emission type display device, a transparent plate which is preferably formed of a glass plate is used as a sealing can in the bottom-emission-type display device.
The organic light emitting phenomenon is a phenomenon which is generated by sandwiching an organic light emitting layer between a lower electrode and an upper electrode and by allowing the organic light emitting layer to emit light with an electric current supplied from upper and lower electrodes. The organic electroluminescent display device which makes use of such a light emitting phenomenon displays a two-dimensional image by arranging a large number of pixels in a matrix array, wherein the organic electroluminescent display device is classified into a passive-matrix-type display device and an active-matrix-type display device depending on a driving method. The passive-matrix-type organic electroluminescent display device is a display device which forms pixels by interposing organic light emitting layers at respective intersecting portion of a large number of scanning lines which extend in one direction and are arranged substantially in parallel to each other on a main surface of an insulating substrate and a large number of signal lines which extend in another direction which crosses one direction and are arranged substantially in parallel to each other on the main surface of the insulating substrate.
On the other hand, the active-matrix-type organic electroluminescent display device includes a large number of scanning lines which extend in one direction and are arranged in parallel to each other on a main surface of an insulating substrate, a large number of signal lines which extend in another direction which crosses one direction and are arranged in parallel to each other, and power source lines. The active-matrix-type organic electroluminescent display device further includes active elements such as thin film transistors (switching elements, hereinafter referred to as thin film transistors) at respective intersecting portions of the scanning lines and the signal lines. Further, an organic light emitting layer (hereinafter also referred to as OLED) is interposed between a lower electrode (pixel electrode) which is driven by the thin film transistor and an upper electrode which is connected to the power source line which supplies an electric current in response to a display signal supplied from the signal line. The active-matrix-type organic electroluminescent display device can eliminate a crosstalk between the pixels thus enabling a multi-gray-scale display with high definition.
FIG. 8 is a cross-sectional view for schematically explaining a constitutional example of the vicinity of one pixel of the organic electroluminescent display device. The organic electroluminescent display device shown in FIG. 8 is the active-matrix-type display device and is constituted such that a thin film transistor TFT is formed on a main surface (inner surface) of a transparent main substrate SUB1 which is preferably made of glass, and an organic light emitting layer OLE is sandwiched between one electrode (anode here) AD which is driven by the thin film transistor TFT and another electrode (here cathode) CD thus constituting a light emitting portion. Here, the thin film transistor TFT is constituted by a poly-silicon semiconductor layer PSI, a gate insulation layer IS1, a gate line (gate electrode) GL, a source-drain electrode SD, an interlayer insulation layer IS2, and an interlayer insulation layer IS3.
The anode AD which constitutes the pixel electrode is formed of a transparent conductive layer ITO which is formed over a passivation layer PSV, and the anode AD is electrically connected with a source-drain electrode SD via a contact hole which is formed between the passivation layer PSV and an interlayer insulation layer IS3. Further, the organic light emitting layer OLE is formed in a recessed portion surrounded by a bank BNK which is formed of an insulation layer applied to the anode AD by applying means such as a vapor deposition method or an ink jet method. Further, using a conductive matted film made of an aluminum thin film, a chromium thin film or the like, a cathode CD is formed in a state that the cathode CD covers the organic light emitting layer OLE and the bank BNK.
This organic electroluminescent display device is referred to as a so-called bottom-emission-type display device, wherein an emitted light L from the light emitting layer is radiated to the outside from a surface of the main substrate SUB1 as indicated by an arrow. Accordingly, the cathode CD is formed of a material which possesses a light reflecting function. To a main surface side of the main substrate SUB1, a sealing glass substrate SUB2 which is also referred to as a sealing can is adhered, and in the inside of a seal which surrounds a peripheral portion not shown in the drawing, nitrogen is filled and sealed.
In the organic electroluminescent display device having such a constitution, as shown in FIG. 9 which is a plan view of an essential part in which a display region is viewed from a first electrode (transparent electrode; anode) side, in a process for forming a large number of pixels PX (organic light emitting elements EL) on the main substrate SUB1, a leak portion LK exists within a pixel opening portion PAP due to a certain reason, and an electric current which contributes to the emission of light flows in the leak portion LK and hence, the organic light emitting element is short-circuited thus giving rise to a case in which a black-dot defective pixel BPX which generates a non-light-emitting region which does not emit light at the time of turning on the panel is generated.
Here, the black-dot defective pixel BPX means a pixel which does not emit light at all times compared to the light emitting element PX which always emits light and constitutes a light emitting region at the time of turning on the panel. Here, in the drawing, symbol PC indicates a pixel circuit, symbol PL indicates a power source line, and symbol GL indicates a gate line.
In the organic electroluminescent display device having such a constitution, as a method of repairing the black-dot defective pixel BPX which is generated within the display region, the laser repair method has been proposed. As a means which repairs the black-dot defective pixel BPX using this laser repair method, U.S. Pat. No. 6,590,335 (patent document 1) discloses a means in which a portion of the metal electrode (cathode) corresponding to the defect is erased by the irradiation of laser beams, and an electric current is allowed to flow in a remaining portion of the defective pixel except for the defective portion thus repairing the defective pixel. Further, Japanese Patent Laid-open 2000-331782 (patent document 2) discloses a means in which a layer which is brought into contact with the transparent substrate among the organic material layer is formed into a leak preventing functional layer which is evaporated due to the absorption of the laser beams, and the metal electrode and the transparent electrode (anode) are separated from each other thus eliminating the occurrence of the leak. Further, U.S. Pat. No. 6,605,372 (patent document 3) discloses a manufacturing method and device in which the whole surfaces of an organic light emitting element in an dark-failure defective pixel or a brightness point defective pixel is irradiated with laser beams and hence, the pixel is insulated whereby the dark-failure defective pixel or the bright-failure defective pixel can be repaired.